I acquired some nice 12/4 Ash and would love to make these into some floating book shelves. My biggest problem right now is that they’re heavy as all get out. Does anyone have any bright ideas on how I could, in essence, hollow them out while still being (or at least giving the allusion that they are) solid pieces of wood. My only thoughts were to slowly and painstakingly either take a forstener bit to them or use my hollow chisel mortiser from the back side.

I guess another way to do it is to use rebar or threaded rod. You could drill out your wall studs, epoxy the rods / bar into place in the stud, then do the same with the ash blank. Maybe leave a slight upward angle to the bar/rod to let it sag itself into place.

How long of a shelf are you talking? How much weight will need to be supported?

Youd be able to hit 3 studs at that point so there’s another option IMO. Hog out a recess in the back of the ash blank and make a cleat out of maple or oak that would fit inside said recess. Lag bolt the cleat into the studs, slide the blank over it, and screw down through the blank into the cleat.

I did my pine 5” x 8” x 6’ fireplace mantle like that. I used tapcons into the brick but im sure lags would be just as strong if not stronger.